1. Field of the Invention
The present invention relates to an infrared absorbent having high light absorption efficiency, an electrophotographic toner including the infrared absorbent, and an electrophotographic image forming apparatus using the toner. More specifically, as for the toner, the invention relates to a light fixing color toner and an invisible toner and, still more specifically, to a light fixing color toner that is easy to fix and an invisible toner that is sensitive to infrared radiation.
2. Description of the Related Art
In an electrophotographic process, an electrostatic latent image is first formed. For example, a photoreceptor, or a photoconductive insulator is imagewise exposed to laser light to eliminate charge on the exposed portions thereof. An electrostatic latent image is thus formed on the photoconductive insulator in accordance with image information. Thereafter, generally, fine powder, a so-called toner, included in a developing agent is adhered to the latent image formed on the photoconductive insulator so as to make the latent image visible. Last, the resulting toner image is electrostatically transferred to a recording medium such as recording paper so as to make printed matter. For fixation of the transferred toner image, a method in which the toner is fused by pressing or heating or both of the two and the fused toner is solidified and fixed, or a method in which light energy is applied to the toner and the resulting fused toner is solidified and fixed is used. The light fixing method utilizing light, which does not cause problems that are caused by pressing or heating has drawn attention. This method is also referred to as a flash fixing method. Such a light fixing method does not require pressing a toner to fix the toner, thereby eliminating the necessity of contacting (pressing) the toner with a fixing roller. Accordingly, there is less deterioration of image resolution (reproducibility) in the fixing process than in a case where pressing is conducted.
Also, the light fixing method does not require heating by a heat source. Therefore, unlike in a heat fixing method, there is not time loss due to not being able to conduct printing from the time that a power source is turned on until a heat source such as a fixing roller is preheated to a desired temperature, and therefore printing can be conducted right after the power source is turned on. Moreover, the light fixing method requires no high-temperature heat source, whereby an increase in the internal temperature of the apparatus can be appropriately prevented.
However, when the light fixing method is used to fix a color toner, which has low light absorption efficiency, the color toner is less easily fixed than a black toner. To improve fixation of the color toner, adding an infrared absorbent to the color toner has been proposed, and many related patent applications have been published (see, for example, Japanese Patent Application Laid-Open (JP-A) Nos. 60-63545, 60-63546, 60-57858, 60-57857, 58-102248, 58-102247, 60-131544, 60-133460, 61-132959, 2000-147824, 7-191492, 2000-155439, 6-348056, 10-39535, 2000-35689, 11-38666, 11-125930, 11-125928, 11-125929, and 11-65167). These patent publications aim to achieve both colorization and light fixation by adding a material absorbing light within the infrared region to the toner as an infrared absorbent.
However, these techniques insufficiently satisfy recent technical demands, and improvement is expected.
Therefore, there is a need for an infrared absorbent having high-efficiency infrared-ray absorbing capability.
There is also a need for an electrophotographic toner including such an infrared absorbent, and specifically for a light fixing color toner with improved fixation efficiency and an invisible toner with improved sensitivity to infrared rays. Also, there is a need for an image forming apparatus using such a toner.